class_docstr: FastAI callback integration.
  Pass an instance of this class to FastAI learner as argument ``cbs``.
  FastAI will call relavent mehtods of this class to log metrics.
code: def after_epoch(self):
      metrics = {}
      try:
          for m in self.learn.metrics:
              if m.value is not None:
                  metrics[m.name] = m.value
      except:
          pass
  
      tracker.save(metrics)
      tracker.new_line()
  
file_path: labml/client/labml/utils/fastai.py
imports: from fastai.callback.core import Callback, patch
  from fastai.learner import Learner
  from labml import tracker
label_desc: Use image node_id 4 for calling the LabMLFastAICallback obj's underlying member method code with example usage: obj.after_epoch() without return types